Shell Programming and Scripting

1 2 3 Abc def ghi
1 2 3 jkl mno p qrts
6 9 0 mno def Abc
7 8 4 Abc mno mno abc 
7 8 9 mno mno abc
7 8 9  mno j k

1 2 3 Abc def ghi jkl mno p qrts
6 9 0 mno def Abc
7 8 4 Abc mno mno abc 
7 8 9 mno mno abc mno j k

awk '{Q=$1 OFS $2 OFS $3;P=$0;$1=$2=$3="\b";A[Q]=A[Q]?A[Q] OFS $0:P} END{for(i in A){print A[i]}}'  Input_file

awk 'FNR==NR{Q=$1 OFS $2 OFS $3;P=$0;$1=$2=$3="\b";A[Q]=A[Q]?A[Q] OFS $0:P;next} (($1 OFS $2 OFS $3) in A){print A[$1 OFS $2 OFS $3]}' Input_file  Input_file

awk '{Q=$1 OFS $2 OFS $3;P=$0;$1=$2=$3="\b";A[Q]=A[Q]?A[Q] OFS $0:P} END{for(i in A){print A[i]}}' input_file
6 9 0 mno def Abc
7 8 4 Abc mno mno abc
7 8 9 mno mno abc mno j k
1 2 3 Abc def ghi jkl mno p qrts

awk 'FNR==NR{Q=$1 OFS $2 OFS $3;P=$0;$1=$2=$3="\b";A[Q]=A[Q]?A[Q] OFS $0:P;next} (($1 OFS $2 OFS $3) in A){print A[$1 OFS $2 OFS $3]}' input_file input_file

1 2 3 Abc def ghi jkl mno p qrts
1 2 3 Abc def ghi jkl mno p qrts
6 9 0 mno def Abc
7 8 4 Abc mno mno abc
7 8 9 mno mno abc mno j k
7 8 9 mno mno abc mno j k

awk 'FNR==NR{Q=$1 OFS $2 OFS $3;P=$0;$1=$2=$3="\b";A[Q]=A[Q]?A[Q] OFS $0:P;next} (($1 OFS $2 OFS $3) in A){print A[$1 OFS $2 OFS $3];delete A[$1 OFS $2 OFS $3]}' Input_file Input_file

1 2 3 Abc def ghi jkl mno p qrts
6 9 0 mno def Abc
7 8 4 Abc mno mno abc
7 8 9 mno mno abc mno j k

awk 'FNR==NR{               #### Here FNR and NR are the awk variables default ones. Where FNR and NR both represents the number of line for Input_file. Difference between FNR and NR is, FNR's value will be RESET whenever awk has completed a Input_file reading and reading another one. 
                                 So FNR==NR condition will be TRUE only when 1st file is getting read because NR's value will be increased till second time Input_file is being read.
Q=$1 OFS $2 OFS $3;         #### Creating a variable named Q, whose value is $1 OFS $2 OFS $3, means field 1st space 2nd field space 3rd field. Where OFS is output field seprator whose defaulkt value is SPACE.
P=$0;                       #### Creating a variable named P whose value is $0(current line's value).
$1=$2=$3="\b";              #### Here I am removing the value of 1st, 2nd and 3rd field is to backspace or setting it to NULL.
A[Q]=A[Q]?A[Q] OFS $0:P;    #### Creating an array here whose index is variable Q($1 $2 $3, as per your requirement), so first value for any index will be complete line and after that it will keep on concatenate the values to it's previous values.
next}                       #### Skip all next statements by awk's in built variable named next.
(($1 OFS $2 OFS $3) in A){  #### Now when 2nd Input_file is being read then this condition will be executed. Where I am checking $1 OFS $2 OFS $3 if they are present in array A then execute following statements.
print A[$1 OFS $2 OFS $3];  #### printing the value of array A whose index is $1 OFS $2 OFS $3, whose value we already got while reading previous Input_file.
delete A[$1 OFS $2 OFS $3]  #### Deleting the value of array A whose index is $1 OFS $2 OFS $3, so that we could avoid duplicate printing the lines.
}'  Input_file   Input_file #### Mentioning the Input_file 2 times to be read.

<BS> FS <BS> FS <BS> FS <rest of record>

awk 'FNR==NR{for(i=4;i<=NF;i++){Q=Q?Q OFS $i:$i};A[$1 OFS $2 OFS $3]=A[$1 OFS $2 OFS $3]?A[$1 OFS $2 OFS $3] OFS Q:Q;Q="";next} (($1 OFS $2 OFS $3) in A){print $1 OFS $2 OFS $3 OFS A[$1 OFS $2 OFS $3];delete A[$1 OFS $2 OFS $3]}'  Input_file  Input_file

1 2 3 Abc def ghi jkl mno p qrts
6 9 0 mno def Abc
7 8 4 Abc mno mno abc
7 8 9 mno mno abc mno j k

awk 'FNR==NR{for(i=4;i<=NF;i++){
                                Q=Q?Q OFS $i:$i
                               };
             A[$1 OFS $2 OFS $3]=A[$1 OFS $2 OFS $3]?A[$1 OFS $2 OFS $3] OFS Q:Q;
             Q="";
             next
            }
     (($1 OFS $2 OFS $3) in A) {
                                print $1 OFS $2 OFS $3 OFS A[$1 OFS $2 OFS $3];
                                delete A[$1 OFS $2 OFS $3]
                               }
    '  Input_file  Input_file

awk 'FNR==NR{for(i=4;i<=NF;i++){                                                     #### Mentioning condition FNR==NR, which will be TRUE when first Input_file is being read. If condition is TRUE then executing the statements into the braces. Where a for loop stars from the variable named i's value from 4 to till the number of fields into that line. 
                                                                                          We are starting from i's value as 4 because first 3 fields are indexes as per your requirement. 
                                Q=Q?Q OFS $i:$i                                      #### We are storing values of all fields apart from $1,$2 and $3 into a variable named Q.
                               };
             A[$1 OFS $2 OFS $3]=A[$1 OFS $2 OFS $3]?A[$1 OFS $2 OFS $3] OFS Q:Q;    #### Creating an array named A whose index is $1 OFS $2 OFS $3 and it's value is concatenating values for common indexes, so for very first time for any index it will be value of Q and then for next time(means when next line comes) it will be concatenated to previous values of array A.
             Q="";                                                                   #### Nullifying the value of variable Q so that it shouldn't be keep on increasing it's value and in next line it's value should be started from scratch only.
             next                                                                    #### Skipping all next statements by using next keyword here.
            }
     (($1 OFS $2 OFS $3) in A) {                                                     #### Now these statements will be executed when second Input_file is being read. If ($1 OFS $2 OFS $3)'s value is present as an index in array A then execute following statements.
                                print $1 OFS $2 OFS $3 OFS A[$1 OFS $2 OFS $3];      #### print the first, second and third field along with the value of array A whose index is current 1st, 2nd and 3rd fields.
                                delete A[$1 OFS $2 OFS $3]                           #### Delete the array A's value whose index is $1 OFS $2 OFS $3, so that duplicate results shouldn't be printed on same indexes for next lines.
                               }
    ' Input_file   Input_file                                                        #### Mentioning the Input_file here 2 times.